An Eco-Friendly N-Doped Carbon Quantum Dot-Based Fluorimetric Assay for Sensitive Betahistine Quantitation in Pharmaceuticals and Biological Fluids.

A rapid, sensitive, and sustainable fluorimetric method based on fluorescence quenching of nitrogen-doped carbon quantum dots (N-CQDs) is introduced for the first time to determine betahistine dihydrochloride (BTH). The N-CQDs were prepared via a simple hydrothermal approach and characterized using transmission electron microscopy for electronic structure and morphology, ultraviolet-visible absorption spectroscopy, energy-dispersive X-ray spectroscopy, and Fourier-transform infrared spectroscopy, confirming their nanoscale structure, elemental composition, and surface functionalization. The N-CQDs gave strong blue emission at 440.0 nm upon excitation at 345.0 nm. BTH-induced concentration-dependent quenching of N-CQDs fluorescence was mainly due to static quenching. Under optimized conditions, the proposed method showed excellent linearity over the concentration range of 0.025-4.00 μg/mL. The method was successfully applied to pharmaceutical dosage forms, content uniformity testing, and urine samples, providing accurate results with satisfactory recoveries and good precision, without interference from common excipients or matrix components. Notably, the procedure operates entirely in distilled water, requiring minimal reagents with a short incubation time, highlighting its simplicity and practicality. The greenness and sustainability of the developed method were quantitatively evaluated and confirmed using the carbon footprint reduction index (CaFRI), the newly developed Nanomaterials Assessment Tool (NAT), and an integrated NQS-SAMI assessment.